osrm-backend/include/vtzero/builder_impl.hpp

#ifndef VTZERO_BUILDER_IMPL_HPP
#define VTZERO_BUILDER_IMPL_HPP

/*****************************************************************************

vtzero - Tiny and fast vector tile decoder and encoder in C++.

This file is from https://github.com/mapbox/vtzero where you can find more
documentation.

*****************************************************************************/

/**
 * @file builder_impl.hpp
 *
 * @brief Contains classes internal to the builder.
 */

#include "encoded_property_value.hpp"
#include "property_value.hpp"
#include "types.hpp"

#include <protozero/basic_pbf_builder.hpp>
#include <protozero/pbf_message.hpp>

#include <cstdlib>
#include <string>
#include <unordered_map>
#include <utility>

namespace vtzero {

    namespace detail {

        class layer_builder_impl {

            // If this layer is copied from an existing layer, this points
            // to the data of the original layer. For newly built layers,
            // this is empty.
            data_view m_data_view{};

            // Buffer containing the encoded layer metadata and features
            std::string m_data;

            // Buffer containing the encoded keys table
            std::string m_keys_data;

            // Buffer containing the encoded values table
            std::string m_values_data;

            protozero::pbf_builder<detail::pbf_layer> m_pbf_message_layer{};
            protozero::pbf_builder<detail::pbf_layer> m_pbf_message_keys{};
            protozero::pbf_builder<detail::pbf_layer> m_pbf_message_values{};

            // The number of features in the layer
            std::size_t m_num_features = 0;

            // Vector tile spec version
            uint32_t m_version = 0;

            // The number of keys in the keys table
            uint32_t m_num_keys = 0;

            // The number of values in the values table
            uint32_t m_num_values = 0;

            // Below this value, no index will be used to find entries in the
            // key/value tables. This number is based on some initial
            // benchmarking but probably needs some tuning.
            // See also https://github.com/mapbox/vtzero/issues/30
            static constexpr const uint32_t max_entries_flat = 20;

            using map_type = std::unordered_map<std::string, index_value>;
            map_type m_keys_index;
            map_type m_values_index;

            static index_value find_in_table(const data_view text, const std::string& data) {
                uint32_t index = 0;
                protozero::pbf_message<detail::pbf_layer> pbf_table{data};

                while (pbf_table.next()) {
                    const auto v = pbf_table.get_view();
                    if (v == text) {
                        return index_value{index};
                    }
                    ++index;
                }

                return index_value{};
            }

            // Read the key or value table and populate an index from its
            // entries. This is done once the table becomes too large to do
            // linear search in it.
            static void populate_index(const std::string& data, map_type& map) {
                uint32_t index = 0;
                protozero::pbf_message<detail::pbf_layer> pbf_table{data};

                while (pbf_table.next()) {
                    map[pbf_table.get_string()] = index++;
                }
            }

            index_value add_value_without_dup_check(const data_view text) {
                m_pbf_message_values.add_string(detail::pbf_layer::values, text);
                return m_num_values++;
            }

            index_value add_value(const data_view text) {
                const auto index = find_in_values_table(text);
                if (index.valid()) {
                    return index;
                }
                return add_value_without_dup_check(text);
            }

            index_value find_in_keys_table(const data_view text) {
                if (m_num_keys < max_entries_flat) {
                    return find_in_table(text, m_keys_data);
                }

                if (m_keys_index.empty()) {
                    populate_index(m_keys_data, m_keys_index);
                }

                auto& v = m_keys_index[std::string(text)];
                if (!v.valid()) {
                    v = add_key_without_dup_check(text);
                }
                return v;
            }

            index_value find_in_values_table(const data_view text) {
                if (m_num_values < max_entries_flat) {
                    return find_in_table(text, m_values_data);
                }

                if (m_values_index.empty()) {
                    populate_index(m_values_data, m_values_index);
                }

                auto& v = m_values_index[std::string(text)];
                if (!v.valid()) {
                    v = add_value_without_dup_check(text);
                }
                return v;
            }

        public:

            // This layer should be a copy of an existing layer
            explicit layer_builder_impl(const data_view data) :
                m_data_view(data) {
            }

            // This layer is being created from scratch
            template <typename TString>
            layer_builder_impl(TString&& name, uint32_t version, uint32_t extent) :
                m_pbf_message_layer(m_data),
                m_pbf_message_keys(m_keys_data),
                m_pbf_message_values(m_values_data),
                m_version(version) {
                m_pbf_message_layer.add_uint32(detail::pbf_layer::version, version);
                m_pbf_message_layer.add_string(detail::pbf_layer::name, std::forward<TString>(name));
                m_pbf_message_layer.add_uint32(detail::pbf_layer::extent, extent);
            }

            ~layer_builder_impl() noexcept = default;

            layer_builder_impl(const layer_builder_impl&) = delete;
            layer_builder_impl& operator=(const layer_builder_impl&) = delete;

            layer_builder_impl(layer_builder_impl&&) = default;
            layer_builder_impl& operator=(layer_builder_impl&&) = default;

            uint32_t version() const noexcept {
                return m_version;
            }

            index_value add_key_without_dup_check(const data_view text) {
                m_pbf_message_keys.add_string(detail::pbf_layer::keys, text);
                return m_num_keys++;
            }

            index_value add_key(const data_view text) {
                const auto index = find_in_keys_table(text);
                if (index.valid()) {
                    return index;
                }
                return add_key_without_dup_check(text);
            }

            index_value add_value_without_dup_check(const property_value value) {
                return add_value_without_dup_check(value.data());
            }

            index_value add_value_without_dup_check(const encoded_property_value& value) {
                return add_value_without_dup_check(value.data());
            }

            index_value add_value(const property_value value) {
                return add_value(value.data());
            }

            index_value add_value(const encoded_property_value& value) {
                return add_value(value.data());
            }

            const std::string& data() const noexcept {
                return m_data;
            }

            const std::string& keys_data() const noexcept {
                return m_keys_data;
            }

            const std::string& values_data() const noexcept {
                return m_values_data;
            }

            protozero::pbf_builder<detail::pbf_layer>& message() noexcept {
                return m_pbf_message_layer;
            }

            void increment_feature_count() noexcept {
                ++m_num_features;
            }

            std::size_t estimated_size() const {
                if (m_data_view.data()) {
                    // This is a layer created as copy from an existing layer
                    constexpr const std::size_t estimated_overhead_for_pbf_encoding = 8;
                    return m_data_view.size() + estimated_overhead_for_pbf_encoding;
                }

                // This is a layer created from scratch
                constexpr const std::size_t estimated_overhead_for_pbf_encoding = 8;
                return data().size() +
                       keys_data().size() +
                       values_data().size() +
                       estimated_overhead_for_pbf_encoding;
            }

            template <typename TBuffer>
            void build(protozero::basic_pbf_builder<TBuffer, detail::pbf_tile>& pbf_tile_builder) const {
                if (m_data_view.data()) {
                    // This is a layer created as copy from an existing layer
                    pbf_tile_builder.add_bytes(detail::pbf_tile::layers, m_data_view);
                    return;
                }

                // This is a layer created from scratch
                if (m_num_features > 0) {
                    pbf_tile_builder.add_bytes_vectored(detail::pbf_tile::layers,
                                                        data(),
                                                        keys_data(),
                                                        values_data());
                }
            }

        }; // class layer_builder_impl

    } // namespace detail

} // namespace vtzero

#endif // VTZERO_BUILDER_IMPL_HPP